Your question is VPN Tunnel Negotiation Phases. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Explain the phases of VPN tunnel negotiation in detail, including what happens at each step.
Cover a practical site-to-site IPsec VPN using IKEv2, and distinguish IKE negotiation from IPsec child-SA establishment and protected data transfer. Explain the packets, cryptographic operations, identities, failure points, and verification signals at each phase. You may briefly contrast IKEv1 or TLS-based VPNs where that clarifies the protocol behavior.